JPS6025163A - Electrode for redox flow battery - Google Patents

Abstract

PURPOSE:To increase the efficiency of the oxidoreductive reaction of a redox flow battery by placing porous complex electrodes consisting of conductive fiber in which active carbon is distributed in the concaves of a positive and a negative graphite electrode. CONSTITUTION:A graphite electrode plate 4 having a concave is placed on one side of each of a positive and a negative electrode 2 facing each other with a diaphragm 3 interposed. Solution passages 6a, 6b, 7a and 7b are formed in the spaces between the positive electrode 1 and the graphite electrode plate 4 and between the negative electrode 2 and the graphite electrode plate 4. Porous complex electrodes 8 are installed in spaces surrounded by the graphite electrode plates 4. They are formed by mixture prepared by homogeneously distributing active carbon 10 in conductive fiber 9 prepared from carbon cloth, graphite cloth or a nonwoven fabric. As a result, the surface area of the contact between the electrode and solution contributing to battery reaction is increased, thereby increasing the efficiency of the reaction of the electrode.

Description

[Detailed description of the invention] , (7) Techniques branch This invention relates to an electrode structure for a redox flow battery.

Redox flow batteries are extremely useful as secondary batteries for power storage.

In order to provide a stable '1 power supply, power must be supplied in accordance with the power demand. Electricity demand fluctuates day and night, seasonally, and weekly. In order to avoid power shortages under any circumstances, the generation capacity must be increased to the maximum value of the power demand. However, building new or expanding power plants requires huge costs and takes a long time, and there are many difficulties associated with this.

Therefore, it is desirable to charge a battery with surplus power when demand decreases without reducing the amount of power generated, and to discharge the power from the battery when demand increases.

Many rechargeable and dischargeable secondary batteries that can temporarily store electricity are already known. Since redox flow batteries have excellent volumetric efficiency, they are suitable as batteries for power storage.

(a) Redox Flow Battery A REDOX FLOW battery uses a redox reaction to store electricity. In a redox reaction, one reactant is oxidized and the other reactant is reduced, which occur simultaneously.

If the redox reaction occurs reversibly, charging and discharging can be performed, so it can be used as a secondary battery.

Two types of ionic solutions are separated by a diaphragm, and positive and negative
Provide electrodes. Each ionic solution can be circulated between a separate tank and an electrolytic cell equipped with an electrode using a pump. When a current is passed between the electrodes, two types of ions undergo oxidation and reduction reactions. The ions whose valence has changed due to the reaction are sent from the electrolytic cell to the tank.

An unreacted ion solution is supplied to the electrolytic cell from another tank, and the ion solution after reaction is stored in the tank mentioned above. An electrolytic cell is simply a space in which redox reactions occur. Electric power is stored in the form of ions in a separate tank. Therefore, volumetric efficiency is good.

An electric power storage system using a redox flow battery will be explained with reference to FIG.

The electricity generated at the power station 11 is transmitted and directly
Some are supplied to load 13, some are supplied to substation equipment 1
2. It is converted to direct current through the impark 14, and is charged with a redundant current.

The redox flow '11L pond consists of a '4 tank 20, a positive electrode 21, a negative electrode 22, a diaphragm 23, and a positive electrode tank 16 turns 16b1 a negative electrode tank 17a117b1 pump 18.1
It consists of 9.

The electrolytic cell 20 is, for example, a liquid (IllA liquid 24 liquid port 4Fe)
/Fe2+hydrochloric acid solution, negative 11ti? ('i 25, Cr2-1-/Cr3+ hydrochloric acid solution is placed, and a gap 11r)% 23 separates the two. The diaphragm 23 allows H, ions or CI ions to pass through, but does not allow positive and negative active ions to pass therethrough.

In this example, the redox reaction at the positive electrode and negative electrode J14 can be expressed by the following equation.

Positive electrode: Fe3+ 10e,: Fe''-negative electrode: Cr
""t-:,: cr3+1e The direction of the reaction is from left to right, which is discharge, and the direction from right to left is charge, reverse 1+jj+. Since the sum of the respective oxidized 'α positions is about 1 volt, a secondary battery with an electromotive force of 1 volt can be created.

Pumps 1B and 19 pump positive and negative electrode liquids into tank 1.
Since it can be fed from 6b to 16a and from tank 17b to 17a (or vice versa), the amount of reactant can be increased to any extent.

Therefore, by increasing the tank capacity, the amount of stored electricity can be increased as much as possible.

The above explanation is for one unit (cell) of a redox flow battery.
It is related to.

In practice, a large number of single cells are connected in series to obtain the required electromotive force. Furthermore, these serially assembled cells are
Connect several in parallel to obtain sufficient current.

In this way, even in a battery including a large number of single cells, the positive and negative electrode liquids have a common flow path and are placed in the same tank 16as 1.
6b% 17as 17b can be used. It is only necessary to provide two liquid flow paths for the positive electrode liquid and the negative electrode liquid, penetrating the assembled cells so as to be perpendicular to each stacked surface of the serially assembled cells.

Of course, the voltage will be applied to the positive electrode 11 and the negative electrode liquid in a divided manner, so 1? There are problems such as corrosion of pipes due to Ii' flakes, and an invention (Japanese Unexamined Patent Publication No. 180081/1981) has been made in an attempt to solve this problem.

Various types of redox flow are known depending on the active ions in the positive and negative electrolytes and the types of solutions that dissolve these ions. Below, the numbers in the 0 brackets indicating the solutions, positive electrode ions, and negative electrode ions indicate changes in ion valence.

(a) Using hydrochloric acid solution Fe (8,/2), Cr (2/3) Fe (
3/2), 'ri (8/4) (b) Those using phosphoric acid solution Mn (3/2), Or (2/3) Mn (3
/2), Cu (1/2) Cr (6/3)
, Cr (2/8) - (C) Using pyrophosphoric acid solution Mn (3/2), Cr (2/8) Cr (6/
8), Cr (2/8) (2) Prior art and its problems It is desirable that the electrolytic cell of a redox flow battery has a volume as small as possible, and that the redox reaction actively occurs.

In reality, the electrolytic cell and electrode are not separate bodies,
An electrode structure is adopted in which a space for the electrolyte is created on the opposing surfaces of the positive and negative electrodes, and the positive and negative electrodes are combined with a diaphragm in between to hold the electrolyte in the space.

FIG. 3 is a sectional view showing the electrode structure of a lucid cell of a conventional redox flow battery.

Both the positive electrode 1 and the negative electrode 2 have the same structure and are almost symmetrical with the diaphragm 3 in between.

Both the positive electrode 1 and the negative electrode 2 have a two-layer structure in which a graphite electrode plate 4 and a porous carbon electrode 5 are combined.

A porous carbon electrode is a carbon conductive cloth or nonwoven fabric, and because it is porous, it can hold electrolytes such as a positive electrode solution and a negative electrode solution.

The porous carbon electrode 5 is arranged in a direction in contact with the diaphragm 3, and the graphite electrode plate 4 has plates J1, 1J surrounding the carbon electrode 5. Since it does not pass through, it also functions as an electrolytic cell 11 that surrounds the electrolyte.As already mentioned, the graphite electrode plate 4 has positive electrode liquid through holes 5, z, and 11.
5 b% ['L polar liquid, rl'fi hole 7a, 7b
etc. are provided so as to communicate at right angles to the laminated surface.

The positive electrode liquid and the negative electrode liquid +i each enter from 6"s 7a into the carbon electrode 5 ('l'lr, l (corresponding to 1'1t'l"I)), pass through this, and go to 6b and 7b. Pass through (or pass in the opposite direction).

Both graphite and carbon are good conductors of electricity, but
Still, such TLT poles had the following drawbacks.

The electrode reaction (oxidation-reduction reaction at the electrode) proceeds more efficiently as the electrode area becomes larger and as the conductivity of the '11i electrode becomes higher.

Carbon, Graphai! A conductive cloth or non-woven fabric such as . Both the li rate is sufficient and it is 4r. For this reason,
The reaction rate was slow, the internal resistance was large, and the charge/discharge efficiency was low.

(1) Structure of the present invention The electrode of the redox flow battery of the present invention is a porous carbon electrode (graphite electrode) to which granular activated carbon is added.
The electrode area is widened.

FIG. 1 is a sectional view showing the electrode structure of the present invention.

Since the electrode structure is similar to the conventional electrode structure shown in FIG. 3, the same reference numerals are used for the same members.

This is the same as the previous example in that the positive electrode 1 and negative electrode 2 face each other with a diaphragm 3 in between, and that a graphite electrode plate 4 with a dish-shaped cross section is used and the electrolyte is passed through the gap created here. Solution through holes 6a% 6b% 7a and 7b are provided in the same manner.

The difference is that instead of providing a porous carbon electrode in the space surrounded by the graphite electrode plate 4,
The point is that a porous composite electrode 8 is provided.

The porous composite electrode 8 consists of conductive fibers 9 and activated carbon 10 distributed therein.

The conductive fiber 9 is a cloth or nonwoven fabric made of carbon or graphite, and the conductive fiber 9 is a cloth or nonwoven fabric made of carbon or graphite. : It is similar to the carbon electrode etc. Carbon cloth is made by gathering and spinning carbon filaments with several diameters of 0.1 to 1. A woven fabric with a thickness of □mm is good.

The activated carbon 10 is preferably activated carbon obtained by granulating carbon particles having a diameter of 0.1 to 1 ηr1i (millimicrons: 10 m) to a particle size of 0.5 to 5 mm. The size of the activated carbon is selected appropriately depending on the size of the electrode of the redox flow battery L cell. The conductivity of activated carbon is preferably 10 to 10Ω.

It is desirable that the activated carbon 10 is evenly distributed over the conductive fibers 9. The activated carbon 10 may be sandwiched between two conductive fibers 9. Alternatively, activated carbon may be attached to one fiber, 1:

In any case, the activated carbon 10 must be bonded to the conductive fiber 9. However, the electrical resistance between the activated carbon 10 and the conductive fiber 9 should not increase due to the bonding. .

To attach activated carbon to conductive fibers, proceed as follows. An adhesive binder such as phenol resin or epoxy phenol resin is used to bond particles and particles to fibers. This is followed by carbonization at 300-700°C in nitrogen.

The organic components in the adhesive are carbonized, and the particles and fibers are integrally molded.

In this way, the conductivity between particles and between particles and fibers is good, and the activated carbon is firmly attached.

Activated carbon is an excellent porous conductive material. Since activated carbon is newly added to the electrode of the present invention, the contact area between the electrode and the solution that contributes to the reaction is significantly increased. The redox reaction at the north pole is greatly promoted. This increases electrode reaction efficiency. In fact, with this electrode structure, redox reactions can occur at a rate about 1.5 times greater than with conventional ones.

Furthermore, since activated carbon is a good conductor of electricity, adding it has the advantage of reducing the internal resistance of the battery.

(Power) Example of implementation An embodiment of the present invention will be explained by iQ.

As the diaphragm 3, the thickness is 0.1, the bond is 100, and the width is 100.
A cation exchange membrane is used between the two.

For 1lli of positive and negative electric current, a mm×1oo mm×1
A combination of a graphite electrode plate of oo my and a carbon cloth (plain weave cloth) of 0.5 order x 70 questions x 7Qy+m was used. There were four parts on one side of the graphite electrode plate, on which two sheets of carbon cloth were laminated.

In the gap between two pieces of carbon cloth, diameter 0 * 5 ”1
Activated carbon made by granulating carbon particles of T (millimicrons) to a particle size of Q, 25 mm was adhered using a phenol resin. As a result, the thickness of the electrode portion was 2.0 mm.

After this, carbonize the adhesive in nitrogen at 500°C and graphite? It is integrally molded with the electrode plate. In this way, the area of the reaction electrode is 70 x 70 mm. The part of the body that touches the electrolytic tank is 2mm x 70mm x
Given in 70 mm.

In this cell, 21 mol of FeCe was dissolved (1
1) A 4N-HC1 solution in which 1 mole of CrCl3 was dissolved was introduced as a negative electrode liquid, and a charge/discharge experiment was conducted.

As a result, it was found that the charge/discharge efficiency increased by at least 5% compared to the conventional one.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the electrode structure of the present invention. Figure 2 is a configuration diagram of a system using redox flow batteries for power storage. Figure @3 is a cross-sectional view showing the electrode structure of a single cell of a conventional redox flow battery. 1 ...... Positive electrode 2 ...... Negative electrode 3 ...... Diaphragm 4 ...... Graphite electrode plate 5・・・
・・・・・・ Porous carbon electrode 6.7・・・・・・
・・・・ Positive electrode liquid, negative electrode liquid through hole 8 ・・・・・・・・・
・ Porous composite electrode 9 ...... Conductive fiber 10 ...... Activated carbon 16a, 16b
... Positive electrode liquid tank 17a, 171)... Negative electrode liquid tank IL19...
... Pump 20 ... Electrolytic cell 21 ... ... Positive electrode 22 ...
... Negative electrode inventor 1-1 Toyokon Hino Mori Fuji [Toshio Matsu Patent applicant Sumitomo Electric-L Co., Ltd.

Claims (2)

[Claims] (1) Separate the positive electrode 1 and negative electrode 2! separated by 43;
In a redox flow battery in which a positive electrode liquid is supplied to the positive electrode 1 and a negative electrode liquid is supplied to the negative electrode 2, a redox reaction is performed reversibly at both electrodes to charge and discharge, both electrodes 1.2 have four parts on one side. A graphite electrode plate 4 and an external porous composite electrode 8 provided on the four parts of the graphite electrode plate 4 are characterized in that the porous composite electrode 8 is made by adding activated carbon 10 to conductive fibers 9. Redox flow battery electrode. (2) The electrode for a redox flow battery according to claim (1), wherein the conductive fibers 9 are carbon cloth or nonwoven fabric.